Add multilingual language and systems learning tracks

en/cpp-foundations-20261101/lesson-3/main.cpp

@@ -0,0 +1,8 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cassert>
+int remaining(int total, int done) { return done >= total ? 0 : total - done; }
+int main() {
+    std::cout << remaining(4, 1) << "\n";
+}